Duct-type indoor units of air-conditioners installed in the ceiling for air-conditioning of the interior of a building or the like have been known. Japanese Patent Application Laid-open No. 2003-42480, for example, describes a duct-type indoor unit of an air conditioner that is concealed in the ceiling. The duct-type indoor unit includes a main body casing having an inlet and an outlet arranged opposite each other, and a heat exchanger and a fan arranged along a straight line between the inlet and the outlet. An inlet duct and an outlet duct are connected to the inlet and outlet of the main body casing, respectively.
The duct-type indoor unit of the air conditioner described in Japanese Patent Application Laid-open No. 2003-42480 has respective ducts connected to the inlet side and outlet side when in use. The fluid resistance thus tends to be high at the inlet and outlet. For this reason, a sirocco fan is commonly used as the fan for achieving a high static pressure. The sirocco fan has an impeller, and a fan casing that houses this impeller.
The fan casing has a spiral shape. The fan casing has an inlet that opens in an axial direction of the impeller, and an outlet that opens at a distal end of a tubular portion extending in a centrifugal direction of the impeller. When the impeller of the sirocco fan rotates inside the fan casing, air is sucked into the fan casing from the inlet, and blown out from the outlet.
One problem with the sirocco fan used in such a duct-type indoor unit of an air conditioner is that it has a large number of components because of the fan casing.
Another problem with the sirocco fan is that it is difficult to improve the fan efficiency without the fan casing, because of the structure wherein air is blown out after first being sucked into the fan casing. This leads to yet another problem that it is difficult to reduce operating power of the fan while securing a necessary level of static pressure and flow amount.